Abstract
Four undervine floor management techniques—composted bark mulch, reflective (white) and black geotextile mulches, and mechanical soil cultivation—were evaluated with regard to weed suppression, canopy sunlight regimes, soil temperatures, vine growth, and fruit composition of Pinot noir at an organically managed vineyard in the Finger Lakes Region of New York during 2004 and 2005. Composted bark mulch and black or white geotextiles significantly reduced weed biomass compared with cultivation, but did not affect vine vigor or overwintering primary bud survival in either year. Vines mulched with white geotextile had significantly greater yields, but there were few differences among treatments in ripening time or fruit composition at harvest. The white geotextile increased yields in one year of this experiment, but those yield increases did not compensate for the higher costs of geotextiles compared with the grower’s standard practice of mechanical soil cultivation.
As concerns about environmental problems increase, more ecologically sustainable systems of food and beverage production are required. Organic agriculture represents one response to this challenge, and there are now more than 5900 hectares of vineyards in the United States managed under organic regulations that prohibit the use of synthetic pesticides and fertilizers, relying instead on naturally derived pesticides and alternative methods for nutrient supply and weed control. In North America, organic viticulture is especially difficult in the humid East where rainfall usually occurs throughout the growing season. High humidity and persistent rainfall during the summer aggravate fungal disease problems, prolong vine shoot growth after veraison, and promote weed growth throughout the vineyard, making weed and disease management more difficult in humid zones compared with arid regions where vineyard water supply can be regulated by irrigation regimes. Excessive weed competition in vineyards can reduce yields or fruit quality and nutrient-stressed vines may also suffer more bud damage during extreme midwinter cold.
Floor management systems in New York organic vineyards usually involve mechanical cultivation beneath vine rows and periodic mowing or light cultivation of the alleys between vines during spring and summer, often combined with hay mulch or compost applications in the alleys during the dormant season. Overwintering or late summer cover crops are sometimes cultivated in the alleys to suppress problematic weeds, moderate vine vigor, and conserve organic matter in the soil (Ingels et al. 1998). Most vineyards in New York’s Finger Lakes Region are on slopes around the lakes, where frequent soil cultivation may increase soil erosion, threaten water quality in adjacent streams and lakes, and degrade soil organic matter and fertility (Pool et al. 1990). Alternatives to mechanical cultivation are thus important for New York vineyards, especially for organic growers who do not have effective herbicide options for weed control.
Plastic or fabric mulches have improved vine establishment and yield in newly planted vineyards (Godden and Hardie 1981, Stapleton et al. 1989), but little research has been published on the use of reflective mulches and geotextiles (open-weave fabrics that block sunlight and weed growth but permit water infiltration and gas exchange) in established vineyards.
Composted biomass mulches of various types have been used to increase soil fertility and organic matter, water infiltration and retention, and pruning weights in organic vineyards (Pinamonti 1998). Recent research indicates that coarse-textured composts may also provide some weed control (Erhart and Hartl 2002), but there is little published information on this topic. Trials at The Pennsylvania State University have evaluated compost application rates for Chardonnay as well as hybrid wine-grapes (http://fpath.cas.psu.edu/compostguide.pdf). Evaluations of composted wood chips and geotextile mulches over 12 years in eight New York orchards have shown that composted bark mulches and some geotextiles are durable (3 to 5 years), control weed growth, increase soil nutrient and water supply, and often improve fruit yields (Merwin 2003, Merwin et al. 1995).
In the present study, four organically approved under-vine floor-management systems (VFMSs) were evaluated and compared: composted bark mulch, black geotextile mulch, reflective white geotextile mulch, and a grower’s standard vineyard floor management practice (periodic disk cultivation under the vine row and in the drive alleys). The purpose of our study was to determine whether alternative VFMSs could provide useful options for organic vineyard floor management by suppressing weed competition and improving vine growth and nutrition, primary bud survival, fruit composition, and yields.
Materials and Methods
Experimental design.
Seven-year-old Pinot noir vines planted on 101–14 rootstock at Silver Thread Vineyard near Lodi, NY, were used for this experiment. The vineyard soil is a Honeoye series, fine-loamy, mixed, mesic, Glossic Hapludalf, with 5 to 8% slope, facing west. Vines were trained to a pendelbogen (low head-trained, cane pruned) system with vertical shoot-positioning (Pfaff 1976). The experiment was set up using a randomized complete block design with six replicates. Blocking was done across rows so that each treatment within a block was applied to a different row. Treatments were applied to at least four adjacent vines in each plot, and end vines were not used for any measurements except weed cover and biomass.
White and black geotextiles and a composted bark mulch treatment were established on both sides of the vine row, in 1-m wide strips directly beneath vines, as follows: white reflective geotextile (woven plastic, Dewitt Industries, Sikeston, MO) mulch, black geotextile mulch, and 10-cm-deep composted hardwood bark mulch (mixture of mainly Acer, Quercus, and Fraxinus, obtained from a local sawmill). The grower’s standard vineyard floor-management system provided a control treatment for comparisons. This standard control treatment was applied to all of the alleyways between each of our four undervine treatments, and beneath the vine rows in the control treatment plots, so that the vineyard floor treatments differed only within the 1-m-wide strip directly under vine rows. The grower’s standard VFMS included shallow soil cultivation with a light disk harrow several times each growing season under the vine rows, shallow cultivation of the drive alleys with the same harrow in late spring, mowing the drive alleys monthly during midsummer, hilling up a furrow of soil over the vine graft union from each side of the vine row in early winter and removing it each spring, and applying a 5-cm layer of hay mulch to alternate drive alleys in late autumn each year.
The geotextile treatments were installed in May 2004 and remained in place until the end of 2005, which prevented hilling up soil around vine bases in those treatments during the winter. For installation, the geotextiles were rolled out in the alleys, slit to the midpoint (0.5 m) from one side next to each vine, moved laterally to fit snugly around each vine base, and then overlapped and secured with metal staples within the vine rows to eliminate gaps in coverage. Both outer edges of the geotextiles were then secured by disking a light furrow of soil about 10 cm wide and 5 cm deep over the fabric edge, from each side of the vine row.
Light and temperature measurements.
Sunlight and temperature were measured from June through October in 2004 and 2005. Ambient and reflected sunlight (micro-mol photosynthetic irradiance m−2 sec−1) in the vine cluster zone were recorded at biweekly intervals with an LI-191 line quantum sensor and LI-250A light meter (LI-COR, Lincoln, NE) as both overhead light (meter pointed upward above clusters) and reflected light (meter pointed down toward the vineyard floor below vines). In 2005, soil temperatures in each section were continuously recorded with miniature data loggers (Kooltrak, Palm Beach Gardens, FL) placed in sealed plastic bags, buried 5 cm below the soil surface in the geotextile and control treatment plots, and placed at the same depth below the bark mulch surface.
Weed cover and biomass.
Weed cover and biomass were measured in June, July, and August 2004 and in June and July 2005. “Weeds” included all vegetation within the vine row (0.5 m on either side of the vines) other than the grapevines. Weed cover was measured with a transect line marked every 4 cm, laid along the vine row 15 cm from the trunks, from end to end of each plot. The presence or absence of weeds at each mark was recorded, and the percentage of weed surface cover was estimated for each section. Weed biomass was measured by manually removing all weeds including shallow roots down to 3 cm below the soil surface, removing all adherent soil and bark debris, and then oven-drying at 70°C to constant dry weight. Weed biomass was calculated as dry biomass per square meter of plot surface. In geotextile and bark mulch plots, all weeds from the entire plot were used for these calculations. In the control treatment plots there were too many weeds to sample the entire plots; thus, a randomly placed 0.6 m2 PVC frame was used to sample representative quadrants of weeds present on each sampling date.
Soil analyses.
Samples were taken from the upper 24 cm of soil beneath vines in August 2004 and July 2005, with a 2-cm-wide soil corer. Four to six cores taken from each plot were stored at 4°C until analysis. A subsample of these cores was taken for determining gravimetric soil water content, and the weight before and after oven-drying was recorded. The remaining soil was sent to the Cornell Nutrient Analysis Laboratory (Ithaca, NY) for analyses of plant nutrient availability, organic matter, and pH. Carbon and nitrogen were measured by the automated combustion method (Horneck and Miller 1998), using an automatic elemental analyzer (ThermoQuest Italia, Milan, Italy). Availability of other essential plant nutrients was estimated by inductively coupled argon plasma spectroscopy of samples extracted in Morgan’s solution (10% [w/v] sodium acetate in 3% acetic acid, buffered to pH 4.8), using a 1:5 (v/v) soil:solution ratio. Soil pH, cation exchange capacity, exchange acidity, and soil organic matter were measured by standard methods (Greweling and Peech 1960, Storer 1984).
Vine water status.
The 2004 growing season in New York was unusually cool and wet, so we did not measure vine water status among the different treatments. The 2005 growing season was unusually warm with a midsummer drought, toward the end of which we measured midday stem water potential on 9 and 18 Aug 2005, and predawn leaf water potential on 19 Aug 2005. For midday readings, one leaf per vine was sampled on sunny days between 1100 and 1300 hr. Each leaf was enclosed in a bag that surrounded its leaf blade, and the bags were wrapped in aluminum foil. After the leaf had been bagged for 1 hour, its stem water potential was measured in the field with a pressure chamber. For predawn readings, one midshoot leaf was selected from each vine between 0330 and 0530 hr, cut from the vine, immediately sealed in a bag, and placed on ice. Leaf water potential was measured in the laboratory immediately upon returning from the site.
Vine size, winter bud survival, and nutrient analyses.
Vine growth was estimated by weight of dormant cane prunings, removing all but three 15-node canes on each vine, as customary for this vineyard. Of the canes removed at pruning time, those from the previous year were separated and weighed. Overwinter bud survival was measured by counting live dormant primary buds on a subsample of the cane prunings in April 2004 and by counting the number of fruitful nodes on the three remaining 15-node canes of each vine in early June 2005.
Vine nutrient status was measured by petiole analysis at bloom for nitrogen, and in mid-August (at veraison) for other essential nutrients, as customary for New York vineyards (Shaulis and Kimball 1956). For each sample, 20 petioles were collected from four vines per plot. The youngest mature leaf from a primary bearing shoot was selected and its leaf blade was removed. Petioles were washed with mild detergent, rinsed, and allowed to dry at 22°C until crisp, and then ground to pass a fine mesh screen. Concentrations of most essential elements were measured by standard methods (inductively coupled argon plasma spectroscopy) at the Cornell Nutrient Analysis Laboratory. Carbon and nitrogen concentrations were measured by the Dumas combustion method (Horneck and Miller 1998) using an automatic elemental analyzer (ThermoQuest Italia).
Harvest, berry sampling, and extraction.
Unusual warmth followed by extreme cold in January 2004 damaged vineyards throughout the Finger Lakes Region, and there was insufficient crop on many vines at our test site for sampling to compare yields that year. By 2005 the vines had recovered, and fruit was harvested for analysis that year. Fifty-berry samples were randomly collected from each plot on 26 Aug, and 100-berry samples were collected on 8 Sept when all remaining fruit was harvested. Samples were weighed immediately after collection. The number of clusters and total weight of fruit were recorded for each vine on 8 Sept 2005. Berries were pressed through cheesecloth with a conical press and wooden pestle. Sugar content of the juice was measured as soluble solids (Brix scale) using a Pocket PAL-1 digital refractometer (Atago, Bellevue, WA). Juice pH was measured with a Symphony SB20 pH meter (VWR, West Chester, PA) and titratable acidity was measured with a DL12 automatic titrator (Mettler-Toledo, Columbus, OH) using 0.1 N NaOH with a titration end point of 8.2.
For whole berry analysis, 30-berry subsamples were removed from the 100-berry samples, cut in half, and stored at −20°C until they were freeze-dried. Freeze-dried berries were ground with mortar and pestle, and extracted according to the method of Kim and Lee (2002). One gram of freeze-dried sample was combined with 10 mL 80% MeOH in a 50-mL centrifuge tube with the headspace filled with nitrogen gas, and placed on a shaker table for 10 min at 80 rpm. The sample was then centrifuged at 4°C at 10,000 rpm for 20 min. The extract was decanted into a 25-mL graduated cylinder and the sample was extracted with another 10 mL 80% MeOH as described above. The MeOH was added to the graduated cylinder to bring it to a volume of 25 mL, the extract was transferred to a 50-mL vial with the headspace filled with N gas and stored at −20°C until analysis.
Fruit analysis for anthocyanins and total phenolics.
Berry extracts were prepared as described previously. Anthocyanins were measured using the pH differential method (Giusti and Wrolstad 2001). Samples were diluted to an absorbance range of 0.1 to 1.0, and all measurements were performed in triplicate. A pH 1.0 buffer was prepared with potassium chloride and a pH 4.5 buffer was prepared with sodium acetate. Each sample was diluted with buffer in a test tube, shaken, and allowed to stand for 30 min. Absorbance was then measured at 520 and 710 nm using distilled water as a blank. Total anthocyanins were calculated as malvidin-3-glucoside using 529 as the molecular weight and 28,000 as the molar absorptivity.
Total phenolic concentrations were determined using a previous method (Singleton and Rossi 1965). Samples were diluted to an absorbance range of 0.1 to 1.0. and all measurements were performed in triplicate with a blank. A 0.2-mL aliquot of sample was added to 2.6 mL distilled water in a test tube. Then 0.2 mL of Folin and Ciocalteu phenol reagent was added and the mixture was shaken. After 6 min, 2 mL 7% Na2CO3 solution was added and the mixture was shaken again. After incubation for 90 min at room temperature, absorbance at 750 nm was measured against a blank. Total phenolic contents were calculated using a standard curve for gallic acid. Values were expressed as mg gallic acid equivalents (GAE) per gram of fresh sample.
Economic analysis.
The cost of each VFMS, excluding hilling up soil over graft unions in winter, was calculated on a per-hectare basis prorated over three years (the projected durability of these geotextiles). Materials costs and labor (at US $10 per hour) for establishing and maintaining each VFMS were included in these calculations, but farm equipment costs (e.g., tractor and disk harrow) and depreciation were not. Time and cost estimates for mowing and cultivation in the control treatments were based on records from Silver Thread Vineyard, and economic surveys of winegrape vineyards in the Finger Lakes Region (White 2005). Treatment costs were based on a vine density of 1994 per hectare, planted at 1.83 m by 2.74 m (vine by row spacing). Relative economic returns for each treatment were based on its average yield for 2005 prorated over three years, compared to the grower’s standard VFMS, assuming a market value of $1764 per ton for organic Pinot noir grapes in New York (based upon prevailing prices in recent years). There was no established price differential for organic versus conventional winegrapes for New York wineries during this study.
Statistical analysis.
Statistical analysis was done with SAS software (SAS Institute, Cary, NC). Because treatment variances were unequal in the reflected sunlight measurements, the Kruskal-Wallis test (proc npar1way) was used to compare differences among treatment means (p = 0.05) for light reflectance. The mixed model procedure (proc mixed) was used to determine significant differences (p = 0.05) among treatments for all other measurements, with blocks considered as random effects. Means separations were performed with the Tukey-Kramer procedure for all data, unless otherwise noted. A regression model (proc reg) was used to analyze components of yield. Graphs were created using SigmaPlot (Systat, San Jose, CA).
Results
Reflected sunlight and soil temperatures.
The white geotextile reflected significantly more sunlight upward from below the vines during June and July 2004, compared with the black geotextile, bark mulch, and control treatments (Figure 1⇓). For the remainder of the 2004 growing season and throughout 2005, there was little difference in reflectance among the VFMS treatments. During 2005, the soil under vines in bark mulch plots remained cooler early in the growing season and warmer later in the growing season, compared with all other treatments (Figure 2⇓). During midsummer there were negligible differences in soil temperature among the treatments. At the end of the 2005 growing season, soil temperatures were several degrees lower in the control treatment compared with all other VFMSs.
Weed cover and biomass.
The black and white geotextiles both reduced weed cover and biomass substantially throughout the 2004 season compared with other treatments, and bark mulch reduced weed cover and biomass compared with the control treatment (Table 1⇓). Weed suppression by all three mulches diminished the following season as weeds encroached on the edges of treatment strips and emerged around the base of some vines; consequently, there were fewer differences in weed cover among treatments in 2005 (Table 2⇓). However, the black and white geotextiles continued to reduce weed biomass throughout 2005 compared with both other treatments, and bark mulch also reduced weed biomass compared with the control treatment.
Soil analyses.
Soil manganese availability was lower under black geotextile compared with the control treatment in 2004 (Table 3⇓) and lower under the black geotextile compared with bark mulch in 2005 (Table 4⇓). Soil in the control treatment had greater NO3-N availability both years and higher NO3-N concentrations compared with all other treatments except the black geotextile in 2004. Although there were no differences in soil organic matter (OM) content among treatments in the first year, there were higher soil OM concentrations under the bark mulch treatment compared with the control and white geotextile treatments a year later in 2005. Soil moisture content was greater under the black geotextile than in control or white geotextile plots in 2004; in 2005, the soil under bark mulch had more soil moisture content than other treatments (Table 4⇓).
Vine water status under drought conditions.
Based on stem and leaf water potentials, it appeared that vines in all treatments were drought stressed in August 2005, after 6 weeks of abnormal heat and negligible rainfall (Table 5⇓). The vines in bark mulch plots generally showed more favorable water status, and those in control plots less favorable status, but there were no significant differences (p = 0.05) in water status among the VFMSs.
Vegetative growth, bud survival, and nutrient analysis.
There were no significant differences in pruning weights or winter bud survival among the VFMS treatments in 2004 or 2005 (data not shown). Vines in bark mulch plots showed increased petiole P levels relative to the control and white geotextile treatments in 2005, but otherwise there were few significant differences in vine nutrient status among the treatments (Table 6⇓).
Fruit composition and components of yield.
There were negligible differences in juice soluble solids, pH, titratable acidity (TA), dry matter content, and anthocyanin or total phenolic concentrations among the treatments in 2005 (Table 7⇓). There were also no significant differences in clusters per vine or average berry weight among the treatments, but the white geotextile plots yielded more total crop per vine, with equivalent fruit quality, compared with vines in black geotextile plots (Table 8⇓). The increased yields in white geotextile plots were attributed to higher cluster weights and more clusters per vine, compared with the other treatments.
Economic analysis.
The bark mulch and geotextile VFMSs were substantially more expensive than the grower’s standard practice in this vineyard, even when treatment costs were projected over the three-year predicted durability of these bark mulch and geotextile mulches (Table 9⇓). Most of the mulch and geotextiles costs were incurred in the initial year of establishment, for purchase and placement of materials. The projected costs for these three alternative VFMSs were actually lower than those for the control treatment during the two subsequent years after installation. White geotextile was the most expensive treatment to establish, but it provided substantial economic benefit (a $2710 increase in estimated annual crop value) relative to the standard undervine floor-management system at this vineyard.
Discussion
Sunlight and temperature.
All four VFMSs reflected about 3 to 6% of ambient sunlight during both years of this study, with little difference between the white reflective mulch and other treatments (Figure 1⇑). The 1-m-wide white geotextile in this experiment reflected much less sunlight than 2- and 5-m-wide strips of the same geotextile in two different experiments that were conducted in other vineyards during the same summers (Hostetler et al. 2007) or an aluminized mulch (Robin et al. 1996). The white geotextile increased sunlight in the cluster zone to the same extent as mechanical or manual leaf removal in other reports (Percival et al. 1994). The relatively small increase in sunlight reflectance by the white geotextile was attributed to its relatively narrow width (1 m) and placement directly beneath the vinerows in our study. There was also a gradual loss of reflectance as the vine canopy filled out and created more shade and as vine leaf litter and surface vegetation debris accumulated on the geotextile surface during the growing season. In June 2004 the white geotextile reflected significantly more sunlight, but by mid-July the reflected sunlight was equivalent in all four treatments. Differences in reflectance were affected more by variable weather conditions (sunny versus cloudy) than by VFMS treatments during the latter half of the growing season.
The bark mulch moderated soil temperatures compared to the other VFMSs, resulting in cooler soil temperatures at the beginning and warmer temperatures at the end of the growing season (Figure 2⇑). Compost mulches have been reported to moderate soil temperatures throughout the season compared with cultivation or a black polyethylene mulch (Pinamonti 1998). We observed slightly higher soil temperatures under black geotextile and slightly lower soil temperatures under white geotextile compared with the control treatment during some of the warmest months, but these differences were not significant. There were no observed differences in subsoil temperature in a study that compared black plastic mulch with an unmulched control, but the black plastic did moderate the maximum and minimum soil temperatures (Van der Westhuizen 1980). In other studies, black plastic mulches significantly increased subsoil temperatures in an open field (Ham et al. 1993) and in a newly planted vineyard (Stapleton et al. 1989). We did not observe these trends at our vineyard, perhaps because the established vine canopies shaded and reduced heat absorption by the black geotextile or because the porous fabric of geotextiles allowed more upward heat dissipation than the solid black plastic films used by other researchers.
Weed cover and biomass.
The black and white geotextiles reduced weed groundcover during the 2004 season and reduced weed biomass in both years (Tables 1⇑ and 2⇑). The weed-suppressive properties of synthetic mulches have also been shown in other crop systems (Bhutani et al. 1994, Bootsma 1988) in comparison with cultivation and herbicides. Although less suppressive than geotextiles, bark mulch in our trials also reduced weed cover and biomass compared with the control, confirming reports that soil with bark mulch at least 5-cm deep had significantly less weed cover than bare soil (Grantzau and Scharpf 1982). Several perennial weeds, including Cirsium arvense (Canada thistle), Asclepias syriaca (milkweed), Digitaria sanguinalis (crabgrass), and Elytrigia repens (quackgrass), were well established at the outset of our experiment and persisted in the bark mulch and control treatment plots. Without such aggressive perennial weeds present, there might have been more sustained weed suppression with bark mulch at this vineyard.
Soil properties and nutrient availability.
There were no differences in soil OM among the treatments in 2004, but one year later soil OM content was greater under bark mulch compared with the control and white geotextile (Table 4⇑). Yao et al. (2005) also found that orchard soils mulched with a similar composted bark had substantially more OM, Ca, P, and cation exchange capacity (CEC) than soils where herbicide or sod had been maintained for 12 years. Pinamonti (1998) reported that mulching with compost increased soil OM; these mulches can provide a sustained increase in vineyard soil OM where that is needed.
The cultivated control treatment had consistently greater soil nitrate levels, which probably resulted from the repeated soil cultivations in this treatment breaking down soil aggregates, incorporating oxygen into the soil, and allowing microbes to mineralize OM and convert ammonium to nitrate (Brady and Weil 1999). Although the other treatments had less available soil N, we saw no treatment differences in petiole N concentrations and no vine symptoms of the N deficiencies that were reported with bark mulch in other studies (Grantzau and Scharpf 1982).
Vine water status.
Others have found that leaf water potential of grapevines was higher with plastic mulching compared with unmulched controls (Ezzahouani 2003, Song and Song 1993), but vines in all our treatments were equally stressed during a prolonged drought in 2005. However, we only measured vine water status in mid-August, eight weeks into a prolonged drought; it is possible that there were treatment differences earlier that summer.
Vine size, bud survival, and petiole nutrient analysis.
We observed no treatment related differences in vine pruning weights during 2004 or 2005. Studies have reported that aluminized mulch increased vine vigor (Robin et al. 1996) and that both black and white plastic mulches significantly increased vine growth (Godden and Hardie 1981, Stevenson et al. 1986, Volosky 1983). In some reports, mulches have enabled young vines to come into production one year earlier (Van der Westhuizen 1980). However, the effects of mulching on soil moisture availability and weed competition may have greater impact on young vines.
Petiole P and K concentrations were higher in vines with bark mulch compared with cultivation treatments in 2005 (Table 6⇑). Other studies have also shown higher availability of these nutrients after mulching with compost or wood chips (Merwin et al. 1995, Yao et al. 2005), although those measured nutrient availability in soil, not the crop. Nearly all essential nutrients in our vines remained in the optimum ranges for V. vinifera both years, and none of our VFMS treatments led to observable vine deficiency symptoms (Robinson 2004).
Fruit composition.
There were no significant differences in fruit soluble solids, pH, TA, anthocyanins, or total phenolics among the different VFMSs (Table 7⇑), unlike some other reports. Robin et al. (1996) found that aluminized mulch increased soluble solids, anthocyanins, and total phenolic concentrations, and others have reported that plastic mulches increased grape sugars and phenolic compounds (El Shamma and Hassan 2001, Ezzahouani 2003, van Leeuwen et al. 1998). Concord vines mulched with oat (Avena sativa) straw reportedly often produced fruit with lower soluble solids than those with sod alley or cultivation treatments (Pool 1990). However, other researchers using black or reflective mulches have reported no effects of mulches on fruit composition (Godden and Hardie 1981, Pearson 2004, Stevenson et al. 1986, Vanden Heuvel and Neto 2006). These contradictory results indicate that mulch effects on fruit composition may depend on grape variety as well as on soil and climatic conditions.
Components of yield.
Although few differences were found in components of yield, in 2005 the white geotextile plots produced substantially more crop per vine than the other treatments (Table 8⇑). In studies of young vineyards, synthetic mulches have increased cluster weights and improved vine yields compared with herbicides (Godden and Hardie 1981, Stevenson et al. 1986), grass sod (Stevenson et al. 1986), cultivation (Volosky 1983), and bare soil (Van der Westhuizen 1980). Some other trials in established vineyards have shown that synthetic mulch increased berry weight, cluster weight, or clusters per vine (Robin et al. 1996, van Leeuwen et al. 1998), but others saw no effects on these components of yield (Ezzahouani 2003, Pearson 2004).
Economic analysis.
The high costs of all three undervine mulch systems were primarily due to materials and labor expenses in the initial establishment year. In the two years after the installation year, the geotextiles and bark mulch would continue to have slightly higher maintenance costs than the control treatment, because it was necessary to replace some areas where the grower’s routine cultivation of midrow alleys damaged geotextile edges or spread some of the bark mulch out of the undervine treatment area. Based on the estimated yields in our experiment, even assuming a three-year functional lifespan for the three mulch treatments, their higher costs were not compensated by increased yields relative to the grower’s standard undervine floor treatment. Despite the substantial yield increase for vines in the white geotextile relative to the control treatment, the potential gains were somewhat lower than those for the much less costly control treatment involving routine cultivation.
Conclusions
In a comparison of four different vineyard floor management systems, the black and white geotextiles were more effective than other approved organic methods at reducing weed cover and biomass in the vine row. However, this potential reduction in weed competition did not improve soil moisture supply, vine water status, vine size, primary bud survival, or fruit composition compared with the grower’s standard system of periodic vineyard floor cultivation. Perennial fruit crops may respond slowly to changes in floor management, so it would be useful to conduct additional studies over longer times.
The reflective white geotextile increased yields without negatively impacting fruit composition, but the higher yields obtained may not offset the additional costs of installing geotextile mulches in comparison with the periodic cultivation used by this organic grower to suppress weeds and release soil nitrogen for vines. Although they are permitted under current USDA organic regulations, geotextiles could be problematic for some organic growers because they represent an expensive off-farm synthetic input. Among the three mulch treatments in our experiment, only the white geotextile provided enough short-term economic benefit to compensate for its relatively high costs. Reflective geotextiles might be useful alternatives to the prevalent organic practice of repeated undervine soil cultivation, especially in young vineyards.
Footnotes
Acknowledgments: The authors thank the Viticulture Consortium–East for funding this research project. Richard Figiel of Silver Thread Vineyard was supportive during two years of research on his farm. Advice for sampling methods and experimental procedures was provided by Drs. Robert Pool, Leroy Creasy, Timothy Martinson, and Andrew Reynolds. Dr. Chris Watkins and Jackie Nock provided lab access and equipment for fruit composition analyses, and Francoise Vermeylen was the consultant for statistical procedures.
- Received November 2006.
- Revision received May 2007.
- Copyright © 2007 by the American Society for Enology and Viticulture